I don't want to put up a long plug but it seems that this may be helpful : We're just about to launch the new iCal-Alarmist 1.3 over here at Knowlegistics (shareware 4€47) which can do just that and more. In case you are still looking just hop over to versiontracker.com or macupdate.com in beginning of February '10 and look for iCal-alarmist. It's been around a long time and even made MacWorld cover CD some years back. End of plug.
In case this is against forum rules I am sorry but I searched the FAQ's and could not find anything against a short notice.
Best
Tim Oldfield
Knowlegistics support

Is there any other way - currently available - to edit multiple events in iCal - so - for example - one can set an alarm for multiple birthdays without having to manually editing each one of them?

iCal Alarmist isnt available just yet.

Thanks!